<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        .container {
            width: 90%;
            height: 600px;
            background: #b0b0b0;
            margin: 0 auto;
            display: flex;
            /*flex-direction: row;  !*默认为主轴方向*!*/
        }
        .left {
            width: 200px;
            height: 100%;
            background: #303ab9;
        }
        .middle {
            flex: 1;
            height: 100%;
            background: #b9191a;
        }
        .right {
            width: 200px;
            height: 100%;
            background: #3f983f;
        }
    </style>
</head>
<body>
    <h1>三列布局</h1>
    <div class="container">
        <div class="left"></div>
        <div class="middle"></div>
        <div class="right"></div>
    </div>
</body>
</html>